The draft report from a WHO/EFSA expert workshop on the threshold of toxicological concern is open for public consultation. The TTC approach centres upon the idea that, even for chemicals with incomplete toxicity profiles, it is possible to predict a level of exposure below which there is no appreciable risk to human health. This level of exposure is defined by a chemical’s structural characteristics (e.g. its Cramer classification). WHO/EFSA’s project aims to recommend improvements and expansions of the Cramer decision tree and TTC approach, and to develop a globally harmonised decision tree for applying the TTC in the risk assessment of chemicals.